Valve



Feb. 1, 1949. l TRAUTMAN l 2,460,774

Filed sepf. 1e, 194s 2 sheets-sheet 2 ATTORNEY UNITED sTATas PATENT orrica 2,46ojz74 vALvn Walter C. Trautman, North Hollywood, Calif.,

assignor, by mesne assignments, to Bendix Aviation Corporation, South Bend, 1nd., a corporation ot Delaware Application September 18, 1943, Serial No. 502,877 9 Claims. (Cl. 137-165) This invention relates to equalizer valves for equalizing the ilow to a plurality of outlets when supplied from a single source. More particularly. the invention relates to a reversible equalizer valve'which will not only divide a fluid flow equally, but will combine several flows into a single stream in equal quantities, both functions being independent of the load or force against which the ilow acts orwhich acts on the now in the reverse direction.

Equalizer valves are useful in many applications. 'I'hey maybe usedto divide a iluld ilow into two or more equal parts for measuring or mixing purposes. In fluid power systems, as in machinery operated by pneumatic or hydraulic fluid under pressure, it may be desirable to have tworemote motors move at the same rate oi speed. When the power iluid is incompressible, such -as hydraulic fluid, equalizer valves can be made to equalize thev rate of speed of two remote motors, regardless of the relative loads imposed upon them.

Equalizer valves are also useful in airplanes` wherein hydraulic uid acts in actuating cylinders to move devices. It is often desirable to have a plurality of items actuated at the same rate of speed. This is particularly true'where the actuated devices might aerodynamically unbalance the airplane by unequal speeds of movement. For example. the uneven retraction of landing gear, or the closing of gear doors or bomb bay doors might seriously affect the airplane when there are unequal loads upon them, as in a cross wind. The most serious problem of equal actuation in airplanes is the ilaps. If these are extended or retracted unevenly during landings or take-offs, they might unbalance the airplane sufliciently to cause a crash. Accordingly, it is common practice to inter-connect the aps by cables running through pulleys. The costly and weighty construction is eliminated by the present invention wherein a single valve may equalize flap movement on both extension and retraction.

Equalizer valves are well known in the fluid actuation art. Nearly all such devices are unidirectional, however; that is, they divide a ilow equally, or they combine equal flows. Very few valves both combine and divide equally, and those that have been available to the public are unsatisfactory. The advantage of such a device is that one valve can do the Work normally requiring two valves. Thus, the present invention can divide flow equally to two actuating cylinders and can recombine liquid ilows in equal amounts, which results in equal movement in both directions, since hydraulic iluid is incompressible for practical consideration. Under the most severe condition, when there is full load on one hydraulic motor, and no load on the other, the present invention will operate with 98% accuracy.

It is therefore an object of the invention to provide a reversible equalizer valve capable of dividing or combining flows equally.

Another object of the 'invention is to provide `a reversible equalizer valve which operates with a high degree of accuracy.

It is an. object of the invention to provide a reversible equalizer valve which is simple in construction, lending itself to inexpensive and high quantity production, and simplifying service.

Other objects and advantages of the invention will be apparent in the following description and claims considered in connection with the accom- Y panying drawings.

In the drawings forming a part of this specification:

Figure 1 is a diagram of a hydraulic system in which the invention is employed;

Figure 2 is a schematic section of the valve' to show the parts and their function;

Fig. 2A is a cross section taken in the plane 2A-2A oi Fig. 2;

Fig. 2B is a cross section taken in the same Figure '7 is a plan view in full section of a modication of the variable orifice means shown in Figure 3.- y

Referring to Figure 1, hydraulic liquid is stored in a reservoir ito which is connecteda conduit i2 delivering-liquid to the inlet oi a power driven pump lil. Pump i4 delivers liquid under pressure to a conduit i8 leading to a four-way valve I8. Also connected to valve i8 is a conduit 20 leading back to reservoir ill to return exhaust liquid. When the iiuid demand is such that iiow 'through the valve is less than the delivery of the pump, delivery fluid is bypassed to the reservoir through a relief valve 22. Leading from valve .I8 is a conduit 24 connected to an equalizer valve 26 forming the invention. From valve 2B conduits 21 and 28 lead to hydraulic actuating cylinor landing gear.

ders 38 and 82 respectively. These actuating cylinders, or hydraulic motors, may be used for any purpose such as retracting and extending flaps Connected to the bottom of cylinders 38 and 82 is a bifurcated conduit 34 connected to four-way valve I8. In the position shown, valve I8 `directs fluid under pressure to equalizer valve 28 where 'the flow is divided equally between cylinders 38 and 82, and the exhaust ow passes through conduit 34 to valve i8, and through conduit 28 to reservoir i8. In the other position of valve I8, fluid under pressure is directed into conduit 34, passing into the lower ends of cylinders 38 and 32. Exhaust flow passes through conduits 21 and 28 to equalizer valve 28 where the flow is combined in equalquantities to direct it through conduit 24 to exhaust.

The valve of this invention is shown in schey matic outline in Figure 2. A valve body 48 has a main fluid port 42, and two branch ports 44 and 46. Placed in port 42 is a piston 48 urged upwardly by a spring 58, the upward movement being restrained by a piston ange 82 engaging an internal shoulder 58. When the fluid pressure overcomes the force of spring 88, the piston 48 will be forced downwardly and the piston moves freely because of a vent 54 to atmosphere from the bottom of main port 42.

Branching from either side of main port 42 are branch conduits 58 and 88 connecting to opposite ends of a transverse bore 88 having an enlarged portion 62, The intersection area of passages 56 and 58 with port 42 are closed varying amounts by piston 48, and these intersections will therefore be described as variable orifices.

`Passages 64 and 65 connect passages 68 and 58 respectively to opposite sides of chamber 62. On both sides of the entrance of passages 68 and 58 into bore' 60 are annular enlargements 66, 81, 68 and 68, the outside two having check valves 18 and 12 connected thereto to stop flow from I bore 68, and the inside two having check valves 14 and 16 permitting ow from borel 88. Each pair of check valves communicates with branch ports 44 and 48 respectively.

Placed in enlarged bore 62 is a piston 'i8 dividing the chamber. Secured to piston 78 are valve rods 88 and 82, having reduced portions 84 and 86 slightly greater in length than the distance between adjacent edges of annular recess pairs 88, 61 and 68, 68. Formed in rods 88 and 82 are holes 86 and 81 communicating the end of the rod with the chamber 82. These holes allow the fluid at the rod ends to escape as the rods aremoved.

The operation of the valve of Figure 2 is as follows: Assuming that fluid under pressure is applied to port 42, the piston 48 will be forced downwardly, uncovering passages 58 and 58 an equal amount. If the flow through each passage is equal, there will be an equal pressure drop through the entrance at piston 48, and these pressures will prevail in the entire valve, balancling the parts and presenting equal resistance to each flow. The advantage of the variable orifice formed by piston 48 is that it enlarges at greater flows because the pressure will be greater, but still it restricts the orifice for small flows to give a pressure drop, This advantage ofa drop producing orifice which is satisfactory under all flow conditions cannot be realized with a, fixed orifice.

Assuming now that one liquid consuming cylinder has a greater load than the other, it will not consume as much liquid as the other cylinder. The flow into its passage, for example passage sages 64 and 66. Since one pressure is greater than the'other, piston 18 and rods 88 and 82 will move towardv the right. By this movement, rod v88 increases the orifice to check valve 14, and rod 82 decreases the orifice to check valve 16 until the drop in pressures in passages 86 and 58 are equalized. During this movement, fluid flows through rod passages 85 and 81 to accommodate valve displacements at the end of the valve rods. If the load or other flow restricting condition applies to the opposite port 48, the corrective motion will be in the opposite direction.

When thevalve rods and 82 are in a neutral position, regardless of whether or not the flows are equal, the clearance orilow areas'into the check valves are so great compared to the area of the metering orifices that there is little or no pressure drop at the valves. When one ow becomes greater than the other, it simply means there is less of a load on that particular cylinder, which is reflected in a lower back pressure in the equalizer valve. The resulting unequal flow results in a shift in the valve mechanism until this greater flow is reduced to equality with the other flow, This valving action is eiiec'tive only because the resultant pressure drop at the restricting valve, added to the back pressure of its cylinder, equals the total back pressure of the cylinder having unrestricted ow. Sincethe flows through the metering orifices are equal, the pressure drops then will be equal. The equalizing action. once established, therefore, is dependent upon a pressure drop at the valve to maintain this action.

The operation in the reverse direction, when the valve re-combines flows, is as follows: Fluid -fiows into the valve through ports 44 and 48. 1 The control metering in this case takes place also at piston 48. Instead of a pressure drop, however, the controlling pressure is back pressure at the orifice compared to a common exhaust pressure present in port 42. During this flow, check valves 14 and 16 are seated and fluid flows around valves 18 and 12, into bore 88 and up passages 56 and 88. Fluid pressure acts on ilange 62 of piston 48, through a passage 55, forcing piston 48 downwardly. Fluid then escapes through the variable orifices formed by piston 48 at port 42.

The exhaust pressure in port 42 being common to bot-h iiows, the drop past piston 48 will increase the pressures in passages 58 and 88 by the amount of the drop. Since the drop increases with ow, the passage having the greatest iiow will have the greatest pressure. This is just the opposite of the condition prevailing when valve 28 splits the flow. For this reason it is'necessary to valve the ow at a different point with the movement of piston I8 in response to pressure.

Therefore, assuming the greater flow is in port 44, and consequently in passage 88, the larger pressure acts to move piston 18 to the left. This movement is-just the opposite from that when the split flow through passage 58 is greater. The control is now efiected by the rod 88 closing the clearance into recess 88. At the same time rod 88 increases the clearance into recess 68. This decreases the greater ow and increases the lesser flow until the two flows are equal. Thus the check valves change the direction of valve actuation 'when the ow is reversed.

During the combining flows, the cylinder with the least load will have an additional amount oi sacem'- iluid pressure. which will be exerted on its respective 'exhaust ilow. tThis results in a greater iiow, and a greater back pressure at the metering orinces, unbalancing the equalizer valve until the valve portion shifts to restrict the greater ow, thereby absorbing the additional amount of fluid pressinfe.l The closing of the valve clearance of this now oi lesser load causes a pressure drop at the valve, which, subtracted from the exhaust pressure o! this cylinder of lesser vfload,l equals the exhaust pressure of the cylinder of the greater load. The ilows being equal, the drops at the metering oriilces will be equal, Thus the valves act to produce a pressure'drop which maintains thelequalizing action ot the invention.

,From the foregoing it is evident that the valves 88 and 82 are important, not only to restrict flow, but to create pressuredrops which exactly compensate in the diierence of loading of the two cylinders being equalized. When the valve splits the fiow the pressure drop at thevalve builds up the back pressure of the cylinder of lesser load. When the equalizer combines ilows, the

v drop atthe valve is subtracted from the exhaust pressure of the cylinder of lesser load, creating an equal, usage of hydraulic energy inboth cylinders, part of the energy being dissipated in work while the remainder, if any, is lost in pressure drop. If this reverse ilow results in a greater.

llow in passage 56, this ow cannot depress piston 43, because the passage is associated with ow' passage 58. In this case, however, when the pressure in passage 58 ls built up, piston 48 will be depressed and the metering action will take place.

If Ithere isany delay of pressure build-up in pas- 35 iiows, it could'readily be altered to produce iiows 40 in any given ratio to each other. Thus the metering orifices may be unequal in size, resultingA in a permanent dislocation of valve actuationn Morespeciflcalm the orifices of the passages 56 and 58 in the wall ofthe cylinder 42 can be made 45 o f diilerent dimensions so that when the piston 48 moves downwardly it will, in any3given position, provide a larger opening into one passage `than the other. As shown in Figs. 2 and 2A, the

oriiics of passages 56 and 58 are circular and of 50 the same diameter toA provide equal pressure drops Jin both passages. In the modication ,shown in Fig. 2B, vthe orifices are rectangular in shape, and the orifice 56| is widerthan the orice 58| so that for any given position of the 55 piston 46, a larger ilow is required through orifice 56| than through oriilce 58| to produce equal pressure drops in the two passages. Where the orifices are of unequal dimensions, they should be rectangular and of the same height for the most accurate results so that the areas exposed by downward movement of the -piston will 'bear thesame ratio in all positions of the piston. However, such accuracy is not always required,

and in somel instances, it is satisfactory to make G5 both orifices circular, but of dierent diameters.

The production embodiment of the equalizer valve of Figure 2 appears in Figures 3 through 6. Referring to Figures 3 and 4, the body of the valve is made in three portlons,preferably castings, a 70 central portion |00, a right hand portion |02 and l ternal step ||2 near the center, and a transverse' This arrangement of parts keeps tube I i6 from' rotating as it reciprocates back and forth.

,The purpose of having sleeve |18 free from v rotation is to insure\ that two drilled metering orifices therein, |24 and .|26, will retain their alignment with transverse bore ||4. Fitted in the lower end oi tubular member I I8 is ailanged piston member |28 urged toward member ||6 by a spring |30 held by an end plug |32. It will be noted that piston |28 has a loose fit in itschamber and that its flange does not engage closely the walls in which it is placed. i' A small passage |33 connects bore with transverse bore I I4,"

municating transverse bore ||4 with a hole |35 at right angles thereto, and hole |36 communicates with a. valve rod recess shown in broken outline. A similarinclined hole |38 in valve body portion |04 connects with a right angle holel |40,

also connecting to the valve rod recess shown in dotted outline. In each body portion are check valve pairs/|42 and |43, 44`and |45, each communicating with the valve rod, recess and termia left hand portion |04. Center portion |00 contalns a main port |06, and each side portion contains branch ports |08 and ||0. Center portion |00 is longitudinally drilled at with an innati'ng in the branch ports ||0 and |08.

Shown in Figure 5 is the manner of connecting valve bodies |04, |00, and |02.. Central body portion |00 has a large transverse bore |46 into which project annular bosses |48 and |50 from body portion |04 and |02 respectively, each retaining a ring seal |49 and 5| to prevent leakage of fluid from bore |46. These members form a cyindrical chamber |41. Inclined bores |34 and |38 are similarly sealed by ring seals |52 and |53. It will also be noted that the upper ends of vertical bores |40 and |36 are sealed by threaded plugs |54 and |55. v

Also shown in Figure 5Y is the valve mechanism. Body members |04 and |02 have holes |56 and 58 which are coaxial. Each hole has annular nica'ting, with `their respective check valves. Placed in holes |56 and |56 and control bore |48 is an integral valve member including a piston portion ,|58 and valve rod portions |51 and |64` having annular reliefs and |66 which a're slightly greater in length than the least distance between the two annular recesses. In a neutral position the clearance into the recesses is about Figure 6 shows the construction of check valves |42 and |43, which is similar to that of check valves |44 and |45.

The operation of the valve of Figures 3 through 6 is similar to that of Figure 2, except for the action of the metering oriidces |24 and |26. When uid enters the valve at main port |56, it

forces' piston |28 outwardlyfrom tubular mem'- plication of net pressure forces to the metering piston |28 and to the tubular member i0 that are proportional to the pressure drop at orifice |28l and are independent of the absolute pressure in any part oi the system.

The construction of the valving mechanism and the pressure responsive mechanisms is very important. A defect of prior equalizers has been the combining of valving and pressure responsive means into one member. Thus a sliding cylinder was exposed to differential pressures developed in the flow path of the fluid. The resulting pressure drops when restricting flow eliminates the eiiect of control pressures produced by a metering oriiice.

vIn the present invention the pressure responsive mechanisms is entirely separate from the valve mechanism and one does not aiect the other. The annular reliefs |65 and |66 on the valve rods form closed chambers with the valve housing insofar as transmitting pressure is concerned. This means that the valves are balanced at all times and this balance is not aiected by valve movement due to the pressure responsive mechanism. 'I'he pressure responsive mechanism is responsive only to difference in the pressures in passages |30 and |40, and is not directly responsive to changing pressures caused by the valve action. As` previously exp1ained, the valves do aifect the back pressures, but only to restore them to an equal basis so that the real control lies in the metering oriiices.

Shown in Figure '7 is a modication of the me- 3, which permits outside tering oriice of Figure adjustment to get exact metering action. An adjustment of this type is very desirable in allowing greater manufacturing tolerances to the various ports controlling this necessarily accurate piece of mechanism. The principle is that of using a piston with an inclined head which piston may be rotated until a condition of equal ilow through the metering oriiices is reached.

A piston |28A has rectangular projections |90 on its flange. The piston |28A is held in place by a compression spring |30A resting on an end lplug |32A of Vcup shape. Plug |32A has longitudinal slots |92 cut in its Wall, and projections |90 of piston |28A fit in these slots |92. Thus, a splined connection is made between the plug and the piston. An external projection |94 on plug |32A is slotted to receive a screw driver. The

-head of piston |28A is inclined as at |96, which inclination may be as little as two degrees from a transverse axis.

The adjustment of the device of Figure '7 is done with a screw driver. The inlet port |06 of the equalizer valve is connected to a source of 'liquid and means to determine equal flow are connected to the branch ports. As the iluid passes through the equalizer, the plug 32A is rotated until the ow is equal. This adjustment vis dependent upon the inclination |96` of the head of pistn |28A. As the piston |28A rotates while depressed by uid pressure, the inclination pre- :ents various surfaces to the oriiices until a condition oi' equality is i'ound as indicated by equal iiows. The seal on plug |32A is compressed at all times and this seal holds the plug in the position to which it is rotated. Thus rotational alignment is maintained throughout the longitudinal stroke oi piston |28A.

It is to be understood that although the most common use of 1. A uid ilow system comprising a common.

line and a pair of branch lines merging with said common line at a junction and having ilow resistance means in each branch adjacent the Junction, and throttling means in each branch spaced from the junction responsive to departure of the pressures in the branches at points therein be- V tween the flow resistance means and thelthrottling means from a given ratio for varying saidy throttling means so as to nullify said departure and maintain the flows in the two branches in constant ratio; in which the throttling means in each branch comprises a pair of passages in parallel, check valve means restricting flow in the two passages to opposite directions, and a pair of throttling valves, one in each passage, s|multaneously operable to close one passage while openine the other, and. vice versa, the construction and arrangement of the throttling means being such that increase in the pressure in either one of the branches relative to the pressure in the other branch eiects increased throttling in.said one 40 branch when the direction of iiow is from the branches into said common line and effects decreased throttling in said one branch when the flow is from the common line into the branches. 2. A fluid iiow system comprising a common line and a pair of branch lines merging with said common line at a junction and having flow resistance means in each branch adjacent the junction, and throttling means in each branch spaced from the junction responsive to departure of the pressures in the branches at points between the ow resistance means and the throttling means from a given ratio for varying said throttling means so as to nullify said departure and maintain the ows in the two branches in constant ratio; in which the throttling means in each branch comprises two passages in parallel, check valve means restricting flow in the two passages in opposite directions, and a pair of throttling valves, one passage while opening the other, and vice versa, the construction and arrangement vof the throttling means being such that increase in the pressure in either one of the branches relative to the pressure in the other branch effects increased throttling in said one branch when the direction of ow is from the branches into said common line and effects decreased throttling in said one branch when the flow is from the common line into the branches, said ow resistance means comprising valve means for variably re- 70 stricting said two branch lines simultaneously, 'spring means urging'said valve means in closing direction, andmeans responsive to diierence in pressure in either direction between said common line and one of said branch lines for opening said valve means. l

the adjustable piston |98 is to. balance the valve for equal flow in the two municating with said respective branch lines, a hollow piston sleeve iltt in said cylinder meinassume nected. to said common line and theother end.

ber for reciprocation the ein andhaving lateral ports registering with saidfrespectivelateral passages at all times, means communicating one end of said sleeve with said common line, a piston reciprocable in said sleeve and adapted to cover and uncover the lateral ports therein, spring .means urging said sleeve in one direction and spring means urging said piston in the `opposite direction wherebynsaid piston normallycovers said ports in said sleeve, means for applying pressure fromone of said branch lines to one end of said sleeve in opposition to the force exerted onsaid sleeve by its associated spring, the other end of the sleeve being exposed to pressure in said common line, the end of said piston opposite, its associated spring means being exposed to the pressure of fluid in said common line and the other end being exposed to the pressure in said v branch line, whereby relative movement between said piston and sleeve to uncover the ports in the sleeve is produced independently by pressure in said common line in excess of the pressure in said one branch line, and by pressure in said branch line in excess of the .pressure in said common line.

4. Aiiuid ilow system comprising a common line and a pair of branch', lines merging with said common line at a junction, and having now resistance means in each 'branch'adjacent the junction, and having throttling means in each branch spaced from the junction responsive to departure of the pressures in the branches at points between 'the iiow resistance ,means and the throttling meansfrom a given ratio for varying said throttling means so as to nullify said departure and maintain the ilows in the two branches in constant ratio; in which said flow resistance means comprise a cylinder member having one end connected to said common line and having two separate ports in its wall connected to said respective branch lines, a piston member in said, cylinder member to variably uncover said ports in response to relative longitudinaimovement between said members, spring means for urging one of said members in direction to cause said piston member to cover said ports, said one member being exposed to fluid pressure in said com- '1o constant ratio: in which said now resistance means comprises a cylinder having one end conconnected to one of said branch lines, and having two separate,l ports in its wall connected to said respective 'branch' lines, a piston in said cylinder to variably uncover said ports in response to relative longitudinal movement thereof, spring means for urging said piston in direction to cover said ports, the edge of the piston which covers and uncovers said ports being so slanted that the order in which said two ports are uncovered in response to relative longitudinal movement between the piston and cylinder, varies according to the position of lrotation of the piston, means determining the position of rotation of said piston while permitting free longitudinal movement thereof, and means'for adjusting said determining means to vary the position of rotation of the piston.

6. A nuid aow system as described in claim 2 in which said flow' resistance means comprises two reciprocable members, one of which has two separate ports in its wall connected to saldrespective branch lines and the other of which is adapted to variably uncover said ports in response to relative sliding movement between said members, said spring means urging said members in opposite directions to cover said ports, stop means limiting movements of said members in their port-closing directions, means4 responsive to difference in pressure in one direction between said common line and one of said branch lines for moving one oi' said members to uncover said ports, and means responsive to diierence in pressure in the opposite direction between said common line and one of l said branch lines for moving the other of said members to uncover said ports, whereby the same portions of said 4k'40 ports are initially uncovered irrespective of the tling means from a given ratio for increasingly mon line at one end and to fluid pressure in one of said Ibranch lines at its opposite end, the edge oi the piston member which covers and uncovers l in the other branch, whereby the ratio of iluid said ports being so slanted that the order in which'g'aid two ports are uncovered by the piston in response to said relative longitudinal movement varies according to the position of relative rotation between said members, means determining the position of relative rotation between said members, and means for adjusting said determining means to vary said position of relative rota-` tion.

5. A fluid ow system comprising a common line and a pair of branch lines merging with said common line at a junction, and having ow resistance means in each branch adjacent the iunction and having throttling means in each branch spaced from the junction responsive to departure throttling the flow in either one of said branches and decreasingly throttling the ow in the'other branch in response to an increase in the pressure in said one'branch relative tothe pressure ow from said branch lines into said common line is maintained substantially constant.

\ 8. A iluid flow system comprising a common line passages, one passage of each pair being in one of the pressures in the branches at points between the ilow resi-,stance means and the throttling, means from a given ratio for varying said throttling means so as to nullify said departure and maintain the ilows in the two branches in branch and the other passage of each pair being in the other branch, said piston including means associated with said iirst'pair of passages for y increasingly throttling the passage in one branch andv decreasingly throttling the passage in the other branch in response to increase of pressure in said one branch relative to that in the bther branch and vice versa, said piston also including means associated with said second pair of `pas sages fori decreasingly throttling the passage in one branch land increasingly throttling the passage in the other branch in response to increase of pressure in said one branch relative to that in the other branch and vice versa, rst means including check valve means for introducing an approximately constant pressure drop, between said common line and said branches and conflnf ing uid flow to said first pairs of passages when the direction of ilow is from said common line into said branches, and second means including check valve means for producing an approximate` ly constant pressure dropbetween said branches and said common line and confining ow to said second pair of passages when the direction of ow is from said branches into said common line.

9. Apparatus for proportioning the flow rates in a pair of branch ducts connected in parallel relation to each other and in series witha common duct containing means for circulating uid in either direction therethrough, said apparatus comprising: iirst' ow control means interconnecting said common duct with said branch ducts for dividing ow from the common duct into the branch ducts in predetermined ratio when the ow through said common duct is in one direction; second ow control means also interconnectins said common duct with said branch ducts for Droportioning ilows from the branch ducts into the common duct in a predetermined ratio when the now through said common duct is in the opposite direction; and means for preventing flow from said branch ducts into said common duct through said rst ilow control means and preventing ow from said common duct into said branch ducts through said second ow control means.

WALTER C. TRAUTMAN.

REFERENCES CITED The following references are of record in the Ille .of this patent:

UNITED STATES PATENTS Montelius Mar. 2, 1948 

